Hydrosilylation chemistry, involving the reaction between a silylhydride and an unsaturated organic group, is the basis for many addition cured products including sealants, elastomers, RTVs, adhesives, and silicone-based coatings. Addition cured silicone formulations are typically comprised of:                (A) an alkenyl substituted polysiloxane that is the primary component or base polymer of the curable composition;        (B) a hydride functional crosslinking silicone, typically a methyl hydrogen siloxane polymer, copolymer or oligomer;        (C) a highly active addition cure hydrosilylation catalyst, typically a platinum (0) catalyst such as Ashby's or Karsedt's;        (D) a cure inhibiting compound or mixtures thereof to increase the useful life of the complete formulation.        
Addition curable silicone formulations of such compositions must have both rapid cure at elevated temperature and an acceptably long working life (i.e., no crosslinking) of the full formulation at or near room temperature. Storage stability may also be an important requirement. These needs are particularly acute for release coating formulations where perhaps the most stringent demand is placed on the catalyst for extremely fast cure at high line coating speeds and very short oven-dwell times (2-5 seconds), together with good bath life of the formulation. Yet, the formulation must essentially completely cure in seconds at elevated temperature to meet release performance requirements on a plethora of different paper and polymeric substrates.
To accommodate these two opposing demands, two part formulations with high platinum loadings and high inhibitor loadings are typically employed in the industry. This current solution has several distinct disadvantages. High platinum catalyst loadings are required in addition curable systems to ensure rapid and complete cure at elevated temperature but this high loading of precious metal catalysts also imparts a significant catalyst cost to the formulation. In addition to cure performance, high platinum catalyst levels are especially needed in release liner applications to ensure adequate anchorage to the substrate. High levels of inhibitors are employed to retard catalyst activity and to extend working life of the formulation at room temperature, but the inhibitors employed may not be rapidly decomplexed from the platinum center at elevated temperature and slow the desired crosslinking reaction at elevated temperature.
A variety of different hydrosilylation catalysts can be used to produce organofunctional silanes and silicone fluids. The catalysts employed in these types of reactions can include Pt (II), Pt (IV) and Pt (0) compounds and complexes the most common being chloroplatinic acid or Karstedt's catalysts. Catalysts for cure reactions, however, require additional characteristics to be successful such as high activity and good-to-excellent solubility in a siloxane matrix. Only platinum (0) compounds such as Ashby's or Karstedt's catalysts easily meet these requirements and are the typical catalysts employed in siloxane crosslinking reactions.
The use of additives to stabilize platinum hydrosilylation catalysts as homogeneous species is an effective way to prevent or reduce active metal loss to aggregation. Steffanut, et al. have reported the use of naphthaquinone derivatives together with Karstedt's catalyst to extend the life of the active Pt during hydrosilylation reactions (Steffanut, P.; Osborn, J. A.; DeCian, A.; Fisher, J. Chem. Eur. J. 1998, 4, 2008.) The use of thiol-containing substrates and/or additives has been reported to enhance the catalysis in hydrosilylation reactions producing organofunctional silanes using highly active substrates such as alkylsilanes or chlorosilanes as the silyl hydride source. Vranken has reported the chloroplatinic acid catalyzed reactions run with homoallylic thioether and PhMe2SiH substrates. The reactions run with substrates containing a thioether functional group displayed higher yields than reactions run with analogous alkyl substituted olefins. (Perales, J. B.; Vranken, D. L. V., Thioether-Directed Platinum-Catalyzed Hydrosilylation of Olefins. J. Org. Chem. 2001, 66 (22), 7270-7274.) Kung demonstrated the use of Et2S additives in Karstedt catalyzed reactions with chlorosilanes and alkylsilanes. The reactions that contained the Et2S additive showed higher yields than those reactions run in the absence of the thioether stabilizer (Downing, C. M.; Kung, H. H., Diethyl sulfide stabilization of platinum complexes catalysts for hydrosilylation of olefins. Catalysis Communications 2011, 12, 1166-1169).
Organic sulfur compounds or sulfur containing siloxanes have been used to produce silicone rubbers that are resistant to degradation in the harsh environments such as fuel cell conditions (i.e., in the presence of H2, O2 and air at high temperatures). Use of compositions which can be crosslinked to give degradation-stable silicone rubbers as sealing compositions in fuel cells has been reported (U.S. Publication No. 2002/0192528). Here, the organosulfur compounds appear to play the role of an anti-oxidant.
Additives that are useful for one type of reaction may not be useful in other systems. This is the case even in hydrosilylation chemistry where materials for use in systems using silanes to provide silylated products cannot be expected to be useful in promoting curing of a vinyl compound with a siloxyhydride. It is also well known that sulfur and its compounds are common poisons to metal catalysts. Further, industry work-horse catalysts such as Karstedt's are prone to partial deactivation via agglomeration, especially at elevated temperatures of use.
In addition to improvements in catalysis, it is often desired to enhance or alter certain material properties of the crosslinked material. In particular, the production of coatings with a highly aesthetic finish or gloss is desired especially in film casting, decorative vinyl covers or coatings of graphic art or decals. To achieve a high gloss finish, the industry typically employs solvent containing formulations (>70% solvent) and slow line speeds or two stage drying setups. The use of solvent is undesirable from a health and operating cost perspective.
It is also desirable to be able to cure silicone coatings at lower temperatures. The high temperatures used in the cure of coatings today is undesirable in terms of cost (heating cost and necessitates additional equipment such as humidifiers, etc in the case of paper substrates) and is not compatible with certain substrates (films with low Tg).